This Kimberley Kamper came in for a service and gave me the perfect opportunity to show how an electro magnet is used within a trailer. brake system.

Magnets are amazing. The forces that pull each other together are so strange and unseen. When we can control them it is even more amazing.

We use electro magnets in so many applications on a 4WD. Cam and crank sensors are basically electro magnets that we use to induce a pulse through a circuit. Same goes with alternators and starter motors, where electro magnets draw (repel) to get a gear system moving. Same goes with winch motors. It’s all magnets and it’s all brilliant.

An electric trailer brake system is one of the most brilliant of all electro magnetic applications. And it’s all controlled by the brakes in the 4WD.

Trailer brake systems have quite a few parts, but in this case I’ll be looking at the brake shoe set up, which is the backing plate that the brake sits on.

The brake shoes themselves have a set of springs to hold them all into position and to bring them back to their rest position. They also have an adjuster at the bottom, to tune the brakes up, and also a large electro magnet that sits on a lever.

When you pull the lever you will see the front brake push out towards the brake drum. This will touch the drum but the way the shoes apply the forces to the brake drum is through a self-energising effect.

The Electro Magnet is attached to the lever behind it. If I pull the magnet to the right the lever will push the brake shoe out to the left. If you can imagine this all happening with the brake drum on this movement will make the brake shoe contact the brake drum applying the brakes and slowing the trailer.

The self-energising effect works by the leading brake shoe making contact with the brake drum.

Then the brake shoe pivots and passes the forces through to the rear shoe which causes the top section of the leading shoe and the bottom section of the trailing shoe to almost jam themselves tighter into the brake.

The rotation of the brake drum also helps these forces to push the shoes tighter which then brakes the trailer.

Where the electro magnet comes into play is, as you press the brake pedal the electric brake controller will energise the magnet which is connected to the lever. The magnet will magnetise itself to the brake drum and the rotation of the drum pulls the lever for the brake shoes which then applies the brakes on the tailer.

The other interesting thing is that the brake controller regulates how much voltage it sends to the magnet. On light applications of the brake pedal it provides less voltage so the magnet doesn’t energise as much but on harder applications it sends a larger voltage which then pulls the magnet on harder and applies the brakes faster and stronger. Most brake controllers also have the option to turn down the strength of braking, from a dial on the controller. This dial will adjust the strength of the voltage directly.

The hand brake however is still controlled by a cable. As you pull on the hand brake lever the cable pulls on the brake shoe lever and pulls the brake shoes out to contact the brake drum and lock the brakes onto position.

This really is just one application of how magnets are used but a good one as it is relatively easy to see how it operates but I have to tell you the way we use and can control electro magnets is brilliant. The future will be very interesting with all of these Hybrid and Electric vehicles.



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